Re: [PATCH v4] mm: fix race between kmem_cache destroy, create and deactivate

[Vladimir Davydov]

On Mon, Jun 11, 2018 at 12:29:51PM -0700, Shakeel Butt wrote:
> The memcg kmem cache creation and deactivation (SLUB only) is
> asynchronous. If a root kmem cache is destroyed whose memcg cache is in
> the process of creation or deactivation, the kernel may crash.
> 
> Example of one such crash:
> 	general protection fault: 0000 [#1] SMP PTI
> 	CPU: 1 PID: 1721 Comm: kworker/14:1 Not tainted 4.17.0-smp
> 	...
> 	Workqueue: memcg_kmem_cache kmemcg_deactivate_workfn
> 	RIP: 0010:has_cpu_slab
> 	...
> 	Call Trace:
> 	? on_each_cpu_cond
> 	__kmem_cache_shrink
> 	kmemcg_cache_deact_after_rcu
> 	kmemcg_deactivate_workfn
> 	process_one_work
> 	worker_thread
> 	kthread
> 	ret_from_fork+0x35/0x40
> 
> To fix this race, on root kmem cache destruction, mark the cache as
> dying and flush the workqueue used for memcg kmem cache creation and
> deactivation. SLUB's memcg kmem cache deactivation also includes RCU
> callback and thus make sure all previous registered RCU callbacks
> have completed as well.
> 
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>

Thanks.